The Sun-Earth Connection

by Amara Graps

"It is true that from the highest point of view the Sun is only one of a
multitude - a single star among millions - thousands of which, most
likely, exceed it in brightness, magnitude, and power. It is only a
private in the host of heaven. But it alone, among the countless
myriads, is near enough to affect terrestrial affairs in any sensible
degree; and its influence upon them is such that it is hard to find the
word to name it." Charles Young 1896 (American astronomer who was the
first to see the green spectral line of solar corona).

In Young's quote above: "to affect terrestrial affairs in any sensible
degree" is an understatement. Our Earth, orbiting 93 million miles away
from the energetic star at the center of the Solar System, receives only
one-half of one-billionth of the Sun's energy output. Mere crumbs! Yet
those "crumbs" are enough to nourish and power the whole planet.

Today, a hundred years after Young's quote, it is still hard to find the
word to name the Sun's influence on our terrestrial affairs. Heat
absorbed by the Sun circulates air currents, which influences ocean
water evaporation which drives clouds and rain, which then adds to vast
rivers that moderates climates. Plant photosynthesis, triggered by the
sunlight, produces carbohydrates which, via the food chain, nourishes
herbivores and carnivores and human beings.

More examples of the Sun's influence on the Earth can be seen via the
interplanetary magnetic field and the solar wind. When the plasma from
the Sun's corona, called the "solar wind," rushes out into
interplanetary space, it contains an imprint of the Sun's magnetic
field. As the Sun rotates, the magnetic field, one line fixed to the
Sun, twists into an Archimedes Spiral shape, reversing its polarity
every eleven years. The rippled sheet triggers aurora and other
electromagnetic disturbances on the Earth as the planets ride the
ripples above and below the solar plane of zero magnetism.

Coronal mass ejections (CME) also trigger aurora and other
electromagnetic disturbances on the Earth. These dramatic discharges of
coronal material contain up to 11,000 million tons of solar matter
traveling at a million miles per hour.

These examples of the Sun's influence on terrestrial affairs still form
an incomplete list. I hope that you can now see why it is difficult find
a word that names the Sun's influence on our Earthly existence!

This article will show you a variety of Internet resources for the
Solar-Earth Connection, from the research projects to the educational to
the playful. Enjoy the ride.

The International Solar Terrestrial Physics (ISTP) program

The International Solar Terrestrial Physics (ISTP) program is a joint
project of the United States, ESA, and Japan to understand the
fundamental processes of the Earth-Sun system. These processes include
stellar convection, magnetic dynamo action, generation of stellar winds,
gravity and fundamental particle physics.

ISTP can be considered a framework for solar-terrestrial science, since
there is now a variety of spacecraft to study the Sun-Earth system. The
spacecraft include SOHO, Geotail, Wind, Polar, and ground-based
observatories. This system is beginning to function extremely well. One
evidence of this efficient system is its ability to observe and quickly
bring together the total picture of coronal mass ejections from the time
that they leave the Sun to the time when they interact with the Earth's
magnetosphere.

In 1997, the news media
published reports about CMEs that left the Sun and were subsequently
tracked by many spacecraft. Not only by the ISTP network, but also
tracked by other spacecraft and observatories. The event in January was
a particularly interesting one because it was the first time that a
solar event had been tracked so thoroughly (from "cradle to grave," said
Stephen Maran at NASA's Goddard Space Flight Center), and it may have
caused the demise of an expensive AT&T satellite which malfunctioned
during the time of the geomagnetic storm following the CME event. The
ISTP link and figure below gives full information about that particular
January CME event, including data, scientific investigations, pictures,
and media reports.

The ISTP page is a good place to start for many Sun-Earth related
information and sites. It is also invaluable to the researcher, because,
not only can you download the latest data from that site, but they also
provide some softare (written in IDL) with which to view and analyze the
data. The ISTP site is also a great place to gather information on CME
events, to learn meetings and reports in the fields related to Sun-Earth
Connections, and finally, I liked their educational outreach links and
their primer on the Earth's magnetosphere. I found a few educational
links that I didn't know about, in particular, a lively and interesting
WWW page about Earth's auroras; created by the San Francisco
Exploratorium (
http://www.exploratorium.edu/learning_studio/auroras)

I give the ISTP page a 9.9 as an example of a useful, interesting, and
educational site.

One of the ISTP spacecraft is the SOHO spacecraft, which stares at the
Sun continuously from a point 1 million kilometers in front of Earth. I
won't go into detail about the large SOHO WWW site now, but I must
mention SOHO because of the large role that the satellite plays in
initial observations of any new solar event. They have a "ringside seat"
on the action, in other words.

The SOHO people are aware of their role in initially spotting solar
disturbances and how that information is used in predicting
subsequequent geomagnetic disturbances on the Earth. They have put
together a WWW page with the latest information from SOHO and links to
pages set up with data from other ISTP spacecraft. You can find that
page at: http://sohowww.nascom.nasa.gov/gallery/current/.

Space Weather

Space weather refers to condtions on the Sun and in the solar wind,
Earth's magnetosphere, ionosphere, and thermosphere that can influence
the performance and reliability of space-borne and ground-based logical
systems and can endanger human life of health.

The Space Environment Center

Many scientists today are working hard at forcasting space weather,
which they aim at being able to predict at least as accurately as they
forecast Earth weather. If scientists can warn a day or so in advance of
an imminent geomagnetic storm, then satellite operators and power
companies can try to protect equipment, averting millions of dollars in
damage.

The Space Environment Center (SEC) in Boulder, Colorado is one of those
groups that works hard at forcasting solar and geophysical events.

They conduct research in solar-terrestrial physics, they develop
techniques for forecasting solar and geophysical disturbances, and they
provide real-time monitoring and forecasting of solar and geophysical
events. This site is an important one because of the breadth of their
offerings. Their offerings include solar-terrestrial data and images, a
daily report of space weather, a report and forecast of Solar
Geophysical Data in an online Web document: "The Weekly", a primer on
the Space Environment with descriptions of the sun and various solar
phenomena, and they have a "Glossary of Solar-Terrestrial Terms", as
well.

One of the most creative educational aspects that I've seen at a solar
physics site is SEC's instruction for
making an origami model of the Sun.
We hope that by putting together this model of the Sun, you can
learn more about the Sun, in particular we hope that you will be able
to answer questions such as "What kinds of cycles does the Sun have?",
"What are the four types of radiation from the Sun?", "What are some
solar features?".

I give this site a 9.9 because of the importance and value of their
scientific offerings to the research and commericial communites. If this
site went away, I can't think of another site that comes close enough to
this one to fill its shoes.

The Space Weather Tutorial Page

The Space Weather Forecast Page in Lund, Sweden, aims at educating the
nonscientist about space weather. My definition for space weather at the
top of this section came from that site.

This WWW site paints a broad picture of the Sun-Earth connection by
touching briefly on each of the important aspects of the connection.
They use a minimum of text and, instead try to teach using colorful
images (in thumbnail form to aid those with slow connections).

The site says that it all starts with solar magnetic flux tubes rising
by magnetic buoyancy. That results in sunspots, solar flares,
prominences, coronal mass ejections, coronal holes, fast solar wind, and
so on. Their images follow that theme. They start with a few brief
descriptions about the interior of the Sun (for example, by providing
descriptions and links to the field of helioseismology, i.e. studies the
solar interior using sound waves.) Then they work outwards with
descriptions and links to the solar chromosphere, the solar corona, out
into interplanetary space, and finally to Earth.

Their last section on that page: "Space weather effects" gives a
pictorial description about the effect of space storms on power systems,
satellite systems, navigation systems, communication systems, manned
space flights and the Earth's climate.

The site is a nicely comprehensive site. They conclude, by summarizing
everything on the Space Weather Tutorial Page (a nice touch!), links
to animations, a glossary of space weather terms, and a bibliography
list for further reading. I thought that the site was very carefully
designed, it was concise, and it portrayed alot of information
in small portions and in a colorful and interesting way. Rating; 9.9

The Solar Guide

The Solar Guide is an Web "users guide" for how to use Geophysical Alert
Broadcasts. The author is David Rosenthal. The guide is based on
information made available by NOAA and the Space Environment Services
Center (site described above). The 45-second Geophysical Alert
Broadcasts are primarily intended for users in North America and the
Pacific, and outline the current nature of the solar-terrestrial
environment.

Updated every three-hours beginning at 0000 UTC, the Geophysical Alert
Broadcasts are concerned with two primary types of Earth-Sun
interaction: electromagnetic radiation and geomagnetic activity (which
includes effects from solar sub-atomic particle emissions).

If you are a researcher in this field or a commercial vendor operating
equipment that could be affected by solar and geomagnetic events, then
you would benefit by knowing about the space weather predictions and how
to interpret the space weather forecasts. This guide well help you in
understanding the lingo of the field. Rating: 9.5

Daily Solar Data

If you are a researcher or an an educator or just simply curious about
how many sunspots are on the Sun today, you can go to this site which
shows daily solar data:

At this site you can download images from some of the major solar
observatories: SOHO, Yohkoh, the National Solar Observatories, and the
High Altitude Observatory, for example. It is a valuable site for the
solar researcher, and it is a valuable site for educators wishing to
show their students the many faces of the Sun. I give it a rating of
9.9 for high content and convenience value.

The Sun

The following WWW site is an educational site by Davison E. Soper at
the University of Oregon about basic aspects of the Sun. It's a
simple, clean, no-frills, high-school level site that is my favorite
example of how the Web should be used for science education.

But the viewer quickly notices that on that page are links with
descriptions about how we know those particular parameters and values.
For example, clicking on the above "Distance" word brings you to another
page that describes astronomical units, and the motion of planets in
elliptical orbits. Clicking on "Luminosity" brings you to a page with a
diagram of the definition of luminosity, an equation and what number
results when one plugs numbers into the simple equation.

I really can't say enough good things about this particular WWW site. I
will mark .1 points off because of the dreary Netscape gray background,
but I wish all sites were full of this much content!
Rating: 9.9

Auroras

Auroras are beautiful light shows visible from those living in Earth's
higher latitudes. The light shows arise from a mixing of trapped solar
charged particles, the Earth's magnetic field, and the Earth's
atmosphere. Charged particles in space from the Sun become pulled into
Earth's magnetic field and are trapped. Once they are trapped, the
particles spiral towards the Earth's magnetic poles, where the particles
hit the gases in the Earth's atmosphere. These collisions give off
energy that we see as colored light.

Many different kind of solar events, such as CMEs can trigger auroras.
During the well-publicized CME events of this last Winter and Spring, the
auroral activity was quite high. There is little doubt at those times that
the activity was caused by the solar storms passing by.

The Aurora Page

This WWW page at Michigan Technological University, Houghton,
Michigan about auroras may be the most comprehensive aurora WWW page
on the Web. Here you will find information, links, and images about
auroras. In particular, you will find easy reading on the subject,
auroral forecasts, many auroral images from the Earth and from space,
auroral sounds, and a long list of other aurora sites. They tie in to
the Sun-Earth connection by providing space and space weather links, as
well. A very useful site for researchers and educators both! Rating 9.9